This invention relates to light emitting devices, in particular to an infra-red light emitting metal-oxide-semiconductor field effect transistor (MOSFET).
Light emitting devices are widely used in electronics for the emission of optical radiation as a result of electronic excitation. The radiation spectrum may be ultraviolet, visible or infrared. These devices are diodes and are traditionally fabricated with direct bandgap semiconductors. Silicon semiconductor, which is the main material for integrated circuits is not suitable for light emitting purpose, because it is an indirect bandgap material and cannot produce efficient light emission.
An object of this invention is to fabricate a light emitting device in silicon. Another object of this invention is to fabricate a MOSFET which is light emitting. Still another object of this invention is to integrate an infrared light emitting device in an integrated structure.
These objects are achieved in this invention by incorporating an extension to the drain of a MOSFET. This extension is doped with erbium (Er) impurity, which forms a light-emitting center to enhance radiative process in an indirect semiconductor such as silicon. In operation, the electrons generated in the channel of the MOSFET travel toward the drain region where they experience high electric field existing in this region, excite and ionize the Er atoms, which then relax by emitting light in the infrared range of 1.54 xcexcm.